The present invention relates to an apparatus and method for a terminal to receive a service from a neighboring cell if the service cannot be advantageously provided from a cell that is supposed to handle the terminal in a UMTS (Universal Mobile Telecommunications System) type IMT-2000 system. In particular, the present invention relates to an apparatus and method for a terminal to receive a service from a neighboring cell whereby the network checks whether a particular service is being provided by a neighboring cell if the service cannot be provided by a particular cell and informs the information of the neighboring cell that can provide the service, while if the terminal receives information of a neighboring cell because the desired service cannot be properly provided from the cell that is supposed to handle the terminal, a radio bearer that is requested by the neighboring cell is configured for that service, and the service is provided from the neighboring cell.
FIG. 1 illustrates an exemplary basic architecture of a UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a terminal 100 (mobile station, user equipment (UE), etc.), a UMTS Terrestrial Radio Access Network (UTRAN) 120, and a core network (CN) 130. The UTRAN 120 includes one or more radio network sub-systems (RNS) 125. Each RNS 125 includes a radio network controller (RNC) 123, and a plurality of base stations (Node-Bs) 121 managed by the RNC 123. One or more cells exist for each Node B 121.
FIG. 2 illustrates a radio interface protocol architecture that exists in the mobile terminal and in the UTRAN as one pair, for handling data transmissions via the radio interface. Regarding each radio protocol layer, the first layer (Layer 1) is a physical layer (PHY) that serves the purpose of transmitting data over the radio interface by using various radio transmission techniques. The PHY layer is connected with an upper layer, the MAC layer via transport channels, which include a dedicated transport channel and a common transport channel depending upon whether that channel is shared or not.
In the second layer (Layer 2), a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer and a broadcast/multicast control (BMC) layer exist. The MAC layer serves the purpose of mapping various logical channels to various transport channels, as well as performing logical channel multiplexing for mapping a plurality of logical channels to a single transport channel. The MAC layer is connected to a higher layer, the RLC layer, via logical channels, and these logical channels are divided into control channels that transmit control plane information and traffic channels that transmit user plane information.
The RLC layer handles the guaranteeing of the quality of service (QoS) of each radio bearer (RB) and the transmission of the corresponding data thereof. To guarantee the unique QoS of a radio bearer, the RLC layer has therein one or two independent RLC entities for each radio bearer, and provides three types of RLC modes; a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM), in order to support the various QoS. Also, the RLC layer adjusts the data size accordingly such that a lower layer may transmit data over the radio interface, by performing segmentation and concatenation on the data received from an upper layer.
The PDCP layer is located above the RLC layer and allows data that is transmitted by using Internet Protocol (IP) packets, such as IPv4 or IPv6, to be effectively transmitted over a radio interface having a relatively smaller bandwidth. For this purpose, the PDCP layer performs a header compression function, whereby only the absolutely necessary data in the header portion of the data are transmitted, in order to increase transmission efficiency over the radio interface. Because header compression is its basic function, the PDCP layer only exists in the PS (packet switched) domain, and a single PDCP entity exists per each radio bearer (RB) for providing effective header compression function with respect to each PS service.
Additionally, in the second layer (L2), a BMC (Broadcast/Multicast Control) layer exists above the RLC layer for performing the functions of scheduling cell broadcast messages and broadcasting to terminals located in a particular cell.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane, for controlling the parameters of the first and second layers and for controlling the transport channels and the physical channels in relation to the configuration, the re-configuration, and the releasing of the radio bearers (RBs). Here, the RB refers to a logical path provided by the first and second layers of the radio protocol for data transfer between the terminal and the UTRAN. And in general, configuration of a radio bearer (RB) refers to regulating the protocol layers and the channel characteristics of the channels required for providing a specific service, as well as setting their respective specific parameters and operation methods.
When the RRC layer of the terminal and the RRC layer of the UTRAN are logically connected together such that RRC messages can be sent and received, such logical connection is called a RRC connection, and the terminal is said to be in RRC connected state. When the terminal is in RRC connected state, the UTRAN knows the cell in which the terminal is located in, and thus direct control of the terminal is possible. In contrast, when there is no RRC connection between the UTRAN and the terminal, the terminal is said to be in idle state and the UTRAN is not aware of the existence of the terminal, and the core network can determine the location area or routing area (which are larger areas than a cell) in which the terminal is located in. Thus, the existence of an idle state terminal can only be determined in terms of (or in units on large areas (e.g., location areas or routing areas), and in order to receive typical mobile communication services such as voice or data, the terminal must establish an RRC connection and enter into connected state.
Next, multimedia broadcast/multicast service (MBMS) will be described. MBMS refers to a downlink transmission service for providing data services such as, streaming services (e.g., multimedia, video on demand, webcast, etc.) or background services (e.g., e-mail, short message services (SMS), downloading, etc.), to a plurality of terminals by employing a downlink dedicated MBMS bearer service. A single MBMS service is comprised of one or more sessions, and MBMS data is transmitted to the plurality of terminals through an MBMS radio bearer while a session is ongoing.
MBMS can be classified into a broadcast mode and a multicast mode. The MBMS broadcast mode refers to transmitting multimedia data to all users within a broadcast area, which is a region where broadcast service is possible. In contrast, MBMS multicast mode refers to transmitting multimedia data to only a certain specified user group within a multicast area, whereby a multicast area, which is a region where multicast service is possible.
The UTRAN employs a radio bearer to provide a MBMS bearer service to a terminal. The types of MBMS bearers used by the UTRAN include a point-to-multipoint (p-t-m) radio bearer and a point-to-point (p-t-p) radio bearer. Here, the point-to-point radio bearer (RB) is a bi-directional RB that comprises a logical channel DTCH (Dedicated Traffic CHannel), a transport channel DCH (Dedicated CHannel), and a physical channel DPCH (Dedicated Physical CHannel). The point-to-multipoint RB is a uni-directional downlink RB that comprises a logical channel MTCH (MBMS Traffic CHannel), a transport channel FACH (Forward Access CHannel), and a physical channel SCCPCH (Secondary Common Control Physical CHannel). A logical channel MTCH is configured for each MBMS service provided to one cell, and is used to transmit user plane data of a particular MBMS service to a plurality of terminals.
The UTRAN providing the MBMS service transmits via the logical channel MCCH (MBMS Control CHannel), MBMS-related RRC messages, namely, control messages to a plurality of terminals. Here, the MCCH is a point-to-multipoint downlink channel, and is mapped to a transport channel FACH (Forward Access CHannel), while the transport channel FACH is mapped to a physical channel SCCPCH (Secondary Common Control Physical CHannel). Examples of MBMS-related RRC messages transmitted through the MCCH include, MBMS service information and MBMS radio bearer information. Here, MBMS service information transmits to the terminals wishing to receive the MBMS service, an ID (identification) list of MBMS services that are ongoing in a corresponding cell and transmits the type of radio bearer for the corresponding MBMS service. Also, when a particular MBMS service uses a point-to-multipoint radio bearer for a corresponding cell, the MBMS radio bearer information transmits information about the point-to-multipoint radio bearer for that service to those terminals that wish to receive that service.
A terminal that wishes to receive a particular MBMS service by using a point-to-multipoint radio bearer receives MBMS service information through the MCCH. If the MBMS service information received by the terminal instructs that the MBMS radio bearer information should be received for a particular MBMS service, the terminal obtains through the MBMS radio bearer information, the necessary information for configuring a MBMS radio bearer at the terminal for receiving the particular MBMS service. Namely, if the MBMS service information received by the terminal includes the ID of a particular MBMS service, and if the type of radio bearer for the particular MBMS service is informed to be a point-to-multipoint type, the terminal receives the MBMS radio bearer information to obtain the point-to-multipoint radio bearer information, and configures a point-to-multipoint radio bearer at the terminal by using this information.
FIG. 3 shows a process in which a UMTS network provides a particular MBMS service (service 1) by using multicast mode. Also, FIG. 3 depicts an example when the UEs (UE1 and UE2) receive a particular service (service 1). First, the users (UE1 and UE2) desiring to receive a MBMS service must perform a subscription procedure. Here, subscription refers to the acts of establishing a relationship between the service provider and the user.
Also, users (UEs) wishing to receive an MBMS service must also receive a service announcement provided from the network. Here, service announcement refers to the function of informing the terminal about a list (index) of the services to be provided and related information. Also, if the user (UE) intends to receive a multicast mode MBMS service, the user (UE) should join a multicast subscription group. Here, ‘multicast group’ refers to a group of users that receive a specific multicast service, and ‘joining’ means merging with the multicast group that has particular users who wish to receive the specific multicast service. Using this joining procedure, the terminal can inform the UTRAN of its intent to receive the particular multicast data (multicast service). In contrast, for a terminal that has joined a particular multicast group, the procedure for terminating the joining of the multicast group is referred to as ‘leaving’. The above-described subscribing, joining, and leaving procedures are performed for each terminal, and a terminal may perform the subscribing, joining, and leaving procedures before, during, or any time after data transmission.
While a particular MBMS service is in progress, one or more sessions for that service may occur in sequence. Here, a session may be defined in various ways. For example, a session may be each complete episode of a multi-episode drama or a session may be certain portions of a sports program, such as scenes that show goals in a soccer match. When data to be transmitted for a particular MBMS service is generated at the MBMS data source, the core network (CN) 130 informs a session start to the RNC 123. In contrast, when there is no further data at the MBMS data source to be transmitted for a particular MBMS service, the core network (CN) 130 informs a session stop to the RNC 123. Between the session start and the session stop, a data transfer procedure for the particular MBMS service can be performed. Here, only those terminals that have joined a multicast group for the MBMS service may receive data that is transmitted by the data transfer procedure.
In the above session start procedure, the UTRAN that received the session start from the core network (CN) transmits an MBMS notification to the terminals. Here, MBMS notification refers a function of the UTRAN for informing a terminal that the transmission of data for a particular MBMS service within a certain cell is impending. The UTRAN can use the MBMS notification procedure to perform a counting operation that determines the number of terminals that wish to receive a particular MBMS service within a particular cell. The counting procedure is used to determine whether the radio bearer for providing the particular MBMS service should be configured as point-to-multipoint (p-t-m) or point-to-point (p-t-p). For selecting the MBMS radio bearer, the UTRAN internally establishes a threshold value. After performing the counting function, the UTRAN may configure a point-to-point MBMS radio bearer if the number of terminals existing within the corresponding cell is smaller than the threshold value, and may configure a point-to-multipoint MBMS radio bearer if the number of terminals existing within the corresponding cell is greater than or equal to the threshold value.
If a point-to-point radio bearer is to be configured, the UTRAN allocates a dedicated logical channel to each terminal (UE) and sends the data of the corresponding service. If a point-to-multipoint radio bearer is to be configured, the UTRAN uses a downlink common logical channel to send the data of the corresponding service.
In the related art, even if the UTRAN receives a session start for a particular MBMS service from the core network (CN), the service may not be provided from a particular cell due to abnormal operation reasons, such as a shortage of radio resources or network resources, or the like. Thus, if the UTRAN cannot receive an MBMS service from a particular cell, according to the related art, a terminal that exists in that particular cell cannot be provided with the MBMS service even if it subscribed to that MBMS service. Additionally, in the related art, the cell that cannot provide the particular MBMS service does not even provide any notification regarding the particular MBMS service, thus terminals that are located within the cell and that subscribed to that MBMS service cannot even know that the MBMS service has started and thus cannot proceed with any other reception attempts for that MBMS service.